Guys,
I'm having strange oil pressure issues with the V8, on brand new oil (15w40 + 1 litre of Lucas Oil Stabiliser) when cold the oil pressure is 55 PSI dropping to about 12 PSI when hot rising as soon as you give a boot full to about 40/45 PSI, unfortunatley after a couple of outings (4x4 sessions) this will drop to about 20 PSI cold and just above zero when warm and seems to fluctuate as if there was air within the system if you give is a bit of gas. In the past as soon as I change the oil and filter (K & N) the pressure resumes as per original (55/12/40+). Now I have done this twice so far and both times I have achieved better results with new oil but I don't want to have to do this each time I go out. This really makes no sense to me as you either have oil pressure or you don't. I'm not sure if this is just coensidental or there is other issues that is being masked by these symptoms. I have a good quality mechanical oil pressure gauge and a good quality oil pressure light (5 PSI I think).
I have also noted that at steep angles the oil pressure will drop right off (light on) and sometimes struggles to regain until its leveled out again. I have looked on the net and have seen suggestions of running 1/2 to 1 quart extra oil due to slow drain back of the oil but I'm not sure.
My initial thoughts are
1. A partially blocked oil pickup? - unlikely as the engine appears to have been well serviced
2. A worn oil pump? - Doesn't make sense as this would be a constant low pressure result
3. A sticking oil relief valve? - possible but seems strange that new oil changes the results
I pretty much stumped and I'm looking for ideas or whether anyone else has had similar issues and what they did to fix it.
I was looking on the net for a rebuild kit for the oil pump and found this,
http://www.ebay.co.uk/itm/AMC-V8-Motors-OIL-PUMP-PLATE-KIT-NEW-for-AMC-290-thru-401-motors-/140906733397?pt=Vintage_Car_Truck_Parts_Accessories&hash=item20ceb21f55Has anyone used one? Do they do what they say?
Rather than through money at parts that may not be reuired I'm looking for advise first.